1. Field of the Invention
The invention relates to a nuclear reactor fuel assembly having a fuel assembly base, a fuel assembly head, nuclear fuel-containing fuel rods extending parallel to each other and being disposed between the fuel assembly head and the fuel assembly base, a water tube being open at both ends, extending parallel to the fuel rods, gripping and being held at the fuel assembly base at one end and having an elongated extension body at the other end, either a first end of the extension body being screwed into the water tube or the water tube being screwed into the first end of the extension body, and a second end of the extension body gripping and being held at the fuel assembly head.
2. Description of the Related Art
One such nuclear reactor fuel assembly is known from published international application No. W091/13441, corresponding to U.S. application Ser. No. 07/924,056, filed Aug. 28, 1992. The water tube of that known nuclear reactor fuel assembly has one end being screwed into the base of the fuel assembly. Two elongated extension bodies, which are parallel to each other, have first ends being screwed into the other end of the water tube and second ends extending into the fuel assembly head, and they are each screwed to the fuel assembly head with a nut.
When handling the two nuts under remote control, it may be important for the start of the thread on the second ends of the extension bodies to assume a preset position. As a rule, assuming such a preset position does no occur automatically, because the production of rotationally oriented threads at both ends of the elongated extension bodies is only possible with great effort. A tolerance range for the alignment of the thread at the first end of the two extension bodies also results when the elongated extension bodies in the water tube are tightened, even if the thread in the water tube were rotationally oriented with respect to the threads at the two ends of the extension body which is screwed into it.
It is accordingly an object of the invention to provide a nuclear reactor fuel assembly, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which enables rotationally oriented fastening of the second end of an elongated extension body on the fuel assembly head with comparatively small effort.
With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor fuel assembly, comprising a fuel assembly base; a fuel assembly head; mutually parallel fuel rods containing nuclear fuel and extending between the fuel assembly head and the fuel assembly base; a water tube having first and second open ends and extending parallel to the fuel rods, the first end of the water tube gripping and being held at the fuel assembly base; an elongated extension body having first and second ends, the second end of the extension body gripping and being held at the fuel assembly head; the second end of the water tube being screwed into the first end of the elongated extension body or the first end of the elongated extension body being screwed into the second end of the water tube; the elongated extension body having two mutually coaxially disposed partial bodies, one of the partial bodies having the second end of the extension body gripping the fuel assembly head and the other of the partial bodies having the first end of the extension body being screwed to the water tube, one of the partial bodies being screwed into the other of the partial bodies.
In an alternative embodiment, a check nut is seated on the one partial body being screwed into the other partial body. The check nut is braced against the other partial body.
The two partial bodies of the elongated extension body can be twisted with respect to each other until the second end of the elongated extension body has the position required for rotationally oriented fastening on the fuel assembly head, which can subsequently be fixed free of play by bracing the check nut against the other partial body.
In accordance with another feature of the invention, the first end of the water tube is screwed into the fuel assembly base.
In accordance with a further feature of the invention, the second end of the extension body extends loosely through the fuel assembly head and the fuel assembly head is fixed on the second end of the extension body by a bayonet connection.
In accordance with an added feature of the invention, there is provided a hollow weld with which the check nut is welded to the one partial body on which the check nut is seated.
In accordance with an additional feature of the invention, the check nut and the one partial body have associated threads being disposed at a distance from the hollow weld.
In accordance with a concomitant feature of the invention, the check nut is welded to the partial body against which the check nut is braced with a lip or V-weld.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a nuclear reactor fuel assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.